1. Field of the Invention
The invention relates to an improved intra-aortic balloon catheter. More particularly, the invention relates to an intra-aortic balloon catheter having a variable diameter inner tube.
2. Description of the Prior Art
Intra-aortic balloon (IAB) catheters are used in patients with left heart failure to augment the pumping action of the heart. The catheters, approximately 1 meter long, have an inflatable and deflatable balloon at the distal end. The catheter is typically inserted into the femoral artery and moved up the descending thoracic aorta until the distal tip of the balloon is positioned just below or distal to the left subclavian artery. The proximal end of the catheter remains outside of the patient""s body. A passageway for inflating and deflating the balloon extends through the catheter and is connected at its proximal end to an external pump. The patient""s central aortic pressure is used to time the balloon and the patient""s ECG may be used to trigger balloon inflation in synchronous counterpulsation to the patient""s heartbeat.
Intra-aortic balloon therapy increases coronary artery perfusion, decreases the workload of the left ventricle, and allows healing of the injured myocardium. Ideally, the balloon should be inflating immediately after the aortic valve closes and deflating just prior to the onset of systole. When properly coordinated, the inflation of the balloon raises the patient""s diastolic pressure, increasing the oxygen supply to the myocardium; and balloon deflation just prior to the onset of systole lowers the patient""s diastolic pressure, reducing myocardial oxygen demand.
IAB catheters may also have a central passageway or lumen which can be used to measure aortic pressure. Typical dual lumen intra-aortic balloon catheters have an outer, flexible, plastic tube, which serves as the inflating and deflating gas passageway, and a central tube therethrough formed of plastic tubing, stainless steel tubing, or wire coil embedded in plastic tubing. A polyurethane compound is used to form the balloon. In this dual lumen construction, the central lumen may also be used to accommodate a guide wire to facilitate placement of the IAB catheter and to infuse fluids, or to do blood sampling.
Very specialized materials, including NITINOL, a kink-resistant superelastic shape memory metal alloy manufactured and sold by Rayehem Corp, and polyimide, have been used for the inner tube in an effort to reduce its outer diameter. A reduced diameter inner tube allows for a reduced diameter of the folded IAB membrane and thus allows for an easier insertion of the IAB catheter into the patient. The benefits of NITINOL and polyimide include their high kink resistance and flexural stiffness at small wall thicknesses compared to the traditional polyurethane material used for prior art inner tubes.
U.S. Pat. No. 6,024,693, herein incorporated by reference, discloses an intra-aortic balloon catheter having a co-lumen tube in which the inner lumen lies between the inner and outer surfaces of the catheter tube. As disclosed in that application a co-lumen arrangement allows for a reduced size catheter having an increased gas path area.
All IAB catheters have two opposing inner tube design considerations. On the one hand, it is desirable to make the outer diameter of the inner tube as small as possible to ensure the maximum gas passage area for rapid inflation and deflation of the balloon. On the other hand, it is desirable to make the outer diameter of the inner tube as large as possible to: (a) ensure proper stiffness of the catheter for insertion of the catheter into the aorta, (b) maintain the pressure transmitting qualities of the inner tube; and to (c) minimize movement of the catheter during pumping.
U.S. Pat. No. 5,456,665 discloses an IAB having an inner tube made from NITINOL. The use of superelastic shape memory materials is widely known. In general, binary compositions of Nickel (Ni) and Titanium (Ti) yield alloys with shape memory and superelastic properties commonly referred to as Nixe2x80x94Ti, NITINOLJ, and other industry names. Use of NITINOL for the inner tube is desirable because a smaller diameter tube can be used while still maintaining the necessary stiffness. However, NITINOL is very expensive, and therefore, there exists a need for an inexpensive intra-aortic balloon catheter having maximum gas passageway cross section and structural properties adequate to resist excessive movement of the catheter during pumping.
The invention is an improved intra-aortic balloon catheter with a balloon membrane, a tip, an inner tube, and an outer tube. The portion of the inner tube disposed within the balloon membrane has a larger outer diameter than the portion disposed within the outer surface of the outer tube. The variable diameter inner tube maximizes the cross sectional area of the gas flow passage, i.e. the annular space between the inner tube and the outer tube, while still assuring adequate stiffness of the inner tube to resist excessive movement during pumping. A portion of the inner tube may optionally be at least partially collapsed during to further increase the gas path area during pumping.
To the accomplishment of the above and related objects the invention may be embodied in the form illustrated in the accompanying drawings. Attention is called to the fact, however, that the drawings are illustrative only. Variations are contemplated as being part of the invention, limited only by the scope of the claims.